Gas turbine engines experience combustion instability during operation at sub-idle conditions, steady state idle, and bursts or snap accelerations from idle. In various gas turbine engine apparatuses, operation at various idle and sub-idle conditions is necessary during transitions between steady state conditions, or during reduced power consumption periods (e.g., turn-down operation or part-load conditions for power generating gas turbine engines). However, combustion instability at or between these conditions generally results in excessive wear or deterioration of the combustion assembly and engine, or generally prevents operation of the gas turbine engine at the desired power output. Inability to operate the gas turbine engine at the desired power output (e.g., part-load) generally results in increased fuel consumption.
Known fuel nozzle assemblies address combustion stability issues via airblast atomizing fuel nozzles, including prefilming airblast atomizers. For example, known fuel nozzle assemblies include introducing a pressurized stream of liquid fuel from a fuel passage onto a solid wall surface (i.e., the prefilming surface). The liquid fuel egresses from a fuel passage as a film along the solid wall surface and is atomized at the edge of the wall by streams of air along the solid wall.
However, known fuel nozzle assemblies, such as those including prefilming airblast structures, may produce undesirable fuel/air re-circulation zones or flame stabilization. Furthermore, the high pressure of liquid fuel egressing the fuel passage may result in undesirable fuel filming on outer sleeve surfaces. Still further, prefilming airblast fuel nozzles including primary and secondary fuel injection may be insufficient to mitigate undesired mixing or collusion of the primary and secondary fuel/air streams.
As such, there is a need for a fuel nozzle structure that mitigates combustion instability, promotes stable part-load operation, and produces desired fuel/air mixing.